ContextResolver doesn't work

@Provider
public class DateResolver implements ContextResolver<ObjectMapper>
{
    private final ObjectMapper mapper;

    public DateResolver()
    {
        mapper = new ObjectMapper();
        mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));
        mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    }

    @Override
    public ObjectMapper getContext(Class<?> type) { return mapper; }
}